wistfully

物憂げにため息をつく

to let out a deep breath expressing a feeling of sad longing

悲しい憧れの気持ちを表す深いため息をつくこと

to look at something for a long time with a feeling of sad longing

to think about something with a feeling of sad longing

物憂げに思い出す

to remember something with a feeling of sad longing

悲しい憧れの気持ちで何かを思い出すこと